Genetic terms

Question 1

Variable expressivity

Answer 1

2 patients with NF1 have VARYING disease SEVERITY

Question 2

Pleiotropy

Answer 2

Pleiotropy is plenty of phenotypes.
One structural gene mutation = multiple phenotypes

PKU leads to light skin, intellectual disability, musty body odor

Question 3

Locus heterogeneity

Answer 3

Albinism

- Mutations in different loci produce similar phenotype

Question 4

Allelic heterogeneity

Answer 4

Beta-thalaessemia

Different mutations SAME LOCUS = same phenotype

Question 5

Codominance

Answer 5

Both alleles contribute to phenotype

• Blood group A, B
• HLA-types
• alpha 1 antitrypsin

Question 6

Incomplete penetrance

Answer 6

BRCA1 doesn’t always result in breast/ovary cancer

Question 7

Autosomal recessive disease with incidence of disorder = 1/10,000. What is the risk of being a carrier (carrier frequency)?

Answer 7

Hardy weinberg: P^2 + 2pq + q^2 = 1 and p+q=1
q^2=1/10,000 so q=1/100
2pq = 1/50 since p is almost always 1

Question 8

Heteroplasmy

Answer 8

Mitochondrial diseases (ragged red fibers, lactic acidosis) - all children of affected mother are affected - will have some normal mitochondria and some abnormal

• variable expressivity in mitochondrial disorder

Question 9

Mosaicism

Answer 9

McCune Albright - not inhereited - problem in mitosis

- cafe au lait with sclerotic fibrotic dysplasia (different cell lines in same individual)

Question 10

Linkage disequilibrium

Answer 10

Two locuses are linked and occur more often - gets broken by recombination events (happen during meiosis)

Question 11

Loss of heterozygosity

Answer 11

Tumor suppressor genes require two hit hypothesis - If patient inherets mutated tumor suppressor gene - the complementary allele has to be deleted for cancer to result (doesn’t happen in oncogenes)

AD tumor suppressor gene – FAP APC, VHL, P53, MEN

Question 12

Uniparental disomy

Answer 12

Only one parent is a carrier of AR disease, but patient gets it

Question 13

Imprinting

Answer 13

Prader Willi and Angelman on Chromosome 15 (one allele always inactivated by methylation, so if uniparental disomy results in disease as well)

• Prader Willi (paternal gene deletion)
• Angelman (maternal gene deletion)

Question 14

slipped strand mispairings

Answer 14

Frameshift mutation (insertion or deletions of nucleotides not divisible by 3) - alters reading frame (can lead to nonsense mutation - Duchenne)

Question 15

Microsatellite instability

Answer 15

Lynch - DNA mismatch repair

Question 16

Indirect ELISA

Answer 16

Detects antibodies in serum against known target antigen

1. Ag to surface of well
2. Pts serum added so Ab can bind Ag
3. Second Ab added (w/enzyme) to attach to patient’s Ab
4. Color changing substrate added

Question 17

Shine delgarno vs kozak sequence

Answer 17

Both are involved with Translation.

Shine delgarno in prokaryotes where start codon is afterwards

Kozak is in eukaryotes where start codon is part of kozak sequence